300 WM OAL Question

[Homer]

Why does the OAL of my loads vary ? Loaded 9 rounds and random check of lengths were : 3.753, 3.749, 3.746, 3.744. Componants were:
R-P cases, 150 gr AccuBond, RCBS dies, Stoney Point OAL gauge(the one with the adapter that mounts on the calipers and you slid the loaded round into the adapter - bullet first), Mitutoyo dial caliper. This situation has come up on other calibers as well.

 

[Innovative]

Homer,

That's a very good question. Many shooters that reload have this problem, and they don't know it. Take a look at this page on our website. You'll see why your OAL measurements are so different. Our website has many other tech tips for making better handloads. Tech Tip about OAL

- Innovative

 

[Homer]

Learn something every day as they say. Thanks for taking the time to provide the info. I have wondered about this for a long time and now I know.

 

[EXPRESS]

Great tip! I have noticed the same problem, though the rifle I shoot most(6PPC) seems to shoot them all just as well.
Just a case of luck really...

 

[wapiti13]

Homer, If you are measuring using a dial caliper off the nose, length will vary as you say. Using a Stoney Point oal gauge (or Sinclair) off the ogive will be more accurate. Still, most bullets will vary +/- .001 or more. /ubbthreads/images/graemlins/frown.gif

 

[Homer]

Re: OAL Doesn\'t Matter

Well, I guess in this case the OAL variance doesn't affect the grouping. Finally got to shoot yesterday and had a 3/8" 3 shot group at 100 yds. Second group was 3/4" but I called the first shot pulled to the left - #2 and #3 almost touching. Load was 150gr AccuBond and IMR 7828 powder. I know this doesn't necessarily mean 3/8" groups every time but it tells me this load/rifle combination is a good one. Will go to the range this week and sight in this combo. Opening day of deer season is in 2 weeks here in Georgia - I will be in my power line stand along with my Win 70 300 mag.

 

[Guest]

There is still one other thing that can cause a difference is the seating of the bullet.
If your cases have a varying degree of "neck" tension, such as a neck that may be real "loose" and one that maybe real "tight". Also the speed at which you move your arm on the press can also make a difference...moving it real slow will at times not seat the bullet to the same depth as if you were to move it real fast.